The present invention relates to simple and efficient piston-actuated drug delivery systems for implantation into an animal or human for delivery of drug to the animal or human incrementally over some period of time.
It is well known in the fields of animal husbandry and veterinary medicine that it is desirable and in some instances necessary to treat or care for farm animals by periodically injecting the animals (or administering orally) with various drugs If a series of injections or other administrations are required, this may require finding and rounding up the animals, administering the desired drug (or different drugs), and then releasing the animals until the next drug administration is due. Of course, it can be time consuming and costly, each time treatment of a farm animal is required, to locate the farm animal and bring it to a suitable location for treatment. It has been proposed that drug delivery devices be implanted in farm animals for the periodic release of drugs, examples of such devices being disclosed in U.S. Pat. Nos. 4,564,363, 4,326,522, 4,425,117, 4,439,197, 3,840,009, 4,312,347 and 4,457,752.
Although the devices disclosed in the above-cited patents serve to deliver a drug or solution to the body of an animal or person in which they are located, the devices are typically limited to specific applications, allow for a onetime discharge (a continuous delivery) of drug into the system of the body in which the device is located, are bulky and therefore difficult to place and maintain in the body, or are complicated and costly to manufacture and use.